The invention relates to a pump assembly for use in a brake system of a vehicle. The pump assembly is intended in particular for use in a hydraulic brake system of a vehicle, where the pump assembly serves the purpose of brake pressure modulation in wheel brake cylinders during slip control or for brake pressure buildup in an electrohydraulic power brake system.
Such pump assemblies today typically have two piston pumps, each with one piston that is received axially displaceably in a cylinder. The two piston pumps are disposed coaxially (boxer arrangement) with the pistons facing one another. Located between the pistons is an eccentric element, which is mounted in a manner fixed against relative rotation on a shaft of an electric motor that is disposed perpendicular to the piston pumps. When the electric motor is turned on, the eccentric element drives the two pistons to execute a reciprocating stroke motion in the cylinders, and this motion brings about the feeding of brake fluid in a manner known per se.
The known pump assemblies have the disadvantage that they are complicated in structure and complex to install and are expensive. Because of the electric motor, the known pump assemblies are large. The electric motor is the dominant member of known hydraulic control circuits, housed in a hydraulic block, of anti-lock brake systems. In addition, the rotary motion of the electric motor has to be converted into a linear reciprocating motion of the pistons of the piston pumps, which involves major shear forces and friction losses, which impair efficiency and cause wear. Yet another factor is a high startup current of the electric motor and a pumping output of piston pumps that does not begin until the engine rpm is increasing. Still another disadvantage of the known pump assemblies is the noise they produce, and with the electric motor a pressure limitation is not possible, so that in the event of a malfunction, very high pressures can occur in the piston pumps, with the attendant risk that the pump assembly will explode.